Heavy-Quarkonium Production in High Energy Proton-Proton Collisions at RHIC

TL;DR

This paper updates the theoretical understanding of heavy-quarkonium production in proton-proton collisions at RHIC, showing that including charm-quark initiated processes aligns predictions with experimental data and impacts heavy-ion collision interpretations.

Contribution

It introduces charm-quark initiated processes into the Color-Singlet model for quarkonium production, which were previously overlooked, improving agreement with experimental results.

Findings

CS model predictions are consistent with data across rapidities.

Charm-quark initiated processes contribute at least 20% to J/Psi yield.

Observation of charm-quark jets opposite J/Psi can confirm these processes.

Abstract

We update the study of the total Psi and Upsilon production cross section in proton-proton collisions at RHIC energies using the QCD-based Color-Singlet (CS) Model, including next-to-leading order partonic matrix elements. We also include charm-quark initiated processes which appear at leading order in alpha_s, but which have so far been overlooked in such studies. Contrary to earlier claims, we show that the CS yield is consistent with measurements over a broad range of J/Psi rapidities. We also find that charm-quark initiated processes, including both intrinsic and sea-like charm components, typically contribute at least 20% of the direct J/Psi yield, improving the agreement with data both for the integrated cross section and its rapidity dependence. The key signature for such processes is the observation of a charm-quark jet opposite in azimuthal angle phi to the detected J/Psi. Our results have impact on the proper interpretation of heavy-quarkonium production in heavy-ion collisions and its use as a probe for the quark-gluon plasma.